RE: Yet even more questions (and I'm sure there'll be more...)

[Williams, Tim <TiJaWi@agron.iastate.edu>]

Rutger Jansma wrote:

> Is this general idea been with us since that long!?! So even it's 
> original describer thought it was probably related to the 
> Marginocephalians. 

Well, the original describers of _Heterodontosaurus_ were Crompton and
Charig back in 1962.  The term 'Marginocephalia' was not coined until 1986
(by Sereno) for a Ceratopsia-Pachycephalosauria clade.  Santa Luca
suggested in a 1980 paper that _Heterodontosaurus_ was not a true
ornithopod, but more closely related to the ceratopsians.  Also it's worth
noting that until cladistic analyses became the norm in the 1980's, the
Ornithopoda was considered to be the ornithischian 'stem-group': the group
from which other ornithischian groups (Stegosauria, Ankylosauria,
Ceratopsia, Pachycephalosauria) were thought to have evolved.  

> This is just one of those cases that the paleontological community 
> (if there is one) is flawed due to overall appearance,

There is no 'last word' on heterodontosaurid relationships - i.e. whether
they are basal ornithopods, basal marginocephalians, or basal to the
Ornithopoda-Marginocephalia split (as Maryanska and Osmolska proposed in a
1985 paper).  Sure, there's evidence that heterodontosaurids could be
marginocephalians, and the idea is intuitively attractive, but phylogenetic
analyses continue to put the heterodontosaurids at the base of the
Ornithopoda.

> as was the 
> case with the basal whales, which were supposed to have evolved from 
> a Mesonychid-like animal, but in truth are more like swimming deers.

Not exactly true.  Whales (Cetacea) and artiodactyls (deers, antelope, pigs,
hippos, camels, etc) are indeed closely related and, based on recently
described fossils, the whales appear to have evolved from very primitive
artiodactyls.  These same fossils (and subsequent analyses) indicate that
the similarities between mesonychids and basal cetaceans ("archaeocetes") is
likely due to convergence.  However, the hypothesis that whales evolved from
*advanced* artiodactyls (within or close to the ruminant clade) - which had
strong support in molecular-derived phylogenies - has very little support
from the fossil record.



Tim



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Timothy J. Williams, Ph.D. 

USDA-ARS Researcher 
Agronomy Hall 
Iowa State University 
Ames IA 50014 

Phone: 515 294 9233 
Fax:   515 294 9359